On Thursday, 30 October 2014 13:56:51 UTC-4, Markus D. wrote:
>
> Hello,
>
> I just stumbled upon a behaviour about associations I do not really
> understand why Rails/ActiveRecord cannot get the connection. Using
> activerecord (4.2.0.beta2).
>
> To describe it, lets work with theses models:
>
> class User < ActiveRecord::Base
> has_many :project_participations
> has_many :projects, through: :project_participations, inverse_of: :users
> end
>
> class ProjectParticipation < ActiveRecord::Base
> belongs_to :user
> belongs_to :project
>
> enum role: { member: 0, manager: 1 }
> end
>
> class Project < ActiveRecord::Base
> has_many :project_participations
> has_many :users, through: :project_participations, inverse_of: :projects
> end
>
>
> A user can participate in many projects with a role as a member or a
> manager. The connecting model is called ProjectParticipation.
>
> I now have a problem using the associations on unsaved objects. The
> following commands work like I think they should work:
>
> # first example
>
> u = User.new
> p = Project.new
>
> u.projects << p
>
> u.projects
> => #<ActiveRecord::Associations::CollectionProxy [#<Project id: nil>]>
>
> u.project_participations
> => #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id:
> nil, user_id: nil, project_id: nil, role: nil>]>
>
>
> So far so good - AR created the ProjectParticipation by itself and I can
> access the projects of a user with u.projects.
>
> But it does not work if I create the ProjectParticipation by myself:
>
> # second example
>
> u = User.new
> pp = ProjectParticipation.new
> p = Project.new
>
> pp.project = p # assign project to project_participation
>
> u.project_participations << pp # assign project_participation to user
>
> u.project_participations
> => #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id:
> nil, user_id: nil, project_id: nil, role: nil>]>
>
> u.projects
> => #<ActiveRecord::Associations::CollectionProxy []>
>
>
> Why are the projects empty? I cannot access the projects by u.projects
> like before, even the ProjectParticipation is there.
>
> But if I go through the participations directly, the project shows up:
>
> u.project_participations.map(&:project)
> => [#<Project id: nil>]
>
> Shouldn't it work like the first example directly:
> u.projects returning me all projects not depending on whether I create the
> join object by myself or not? Or how can I make AR aware of this?
>
>
`u.projects` is going to load things from the database if the record is
saved, but otherwise it will only return objects you've explicitly stored
in it.
The `through` association is not the same as just mapping `&:project` over
project_participations.
Can you describe what you're trying to do in more detail? There's likely a
way to make AR do the right thing.
--Matt Jones
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